For men and women in the United States, colon cancer is the third most common cause of cancer death and the leading gastrointestinal cause of death. Epidemiological and animal studies associate colon cancer risk with alterations in the spectrum and concentration of fecal bile acids. The present line of investigation was initiated by our unanticipated observation that bile acids interact with muscarinic receptors. M3 muscarinic receptors (M3R), which are over-expressed in most colon cancers, are key players in colon cancer cell proliferation. Our data indicate that bile acids interact functionally with M3R expressed on human colon cancer cell lines thereby activating matrix metalloproteinase (MMP)-7, releasing HB-EGF, and inducing transactivation of epidermal growth factor receptors (EGFR). Post-receptor signaling via ERK stimulates human colon cancer cell proliferation. Collectively, these observations identify M3R as a novel therapeutic target to prevent and/or treat colon cancer. The central hypothesis of this revised R01 application is that M3R expression and activation in vivo mediates bile acid promotion of intestinal neoplasia. In mice treated with a procarcinogen [azoxymethane (AOM)] and mice with an apc gene mutation (ApcMin/+ mice), our preliminary findings show that M3R-deficiency reduces intestinal tumor number. Primary goals of the revised research plan are to use these unique murine colon cancer models to establish the importance of M3R expression for development of colon neoplasia, to identify molecular mechanisms whereby bile acid-induced activation of M3R promotes carcinogenesis, and to establish that pharmacologic inhibition of M3R activation mimics m3r gene ablation thereby attenuating intestinal neoplasia. To test our central hypothesis and address these goals we propose three focused Specific Aims: Aim 1. Establish the critical role of M3R expression for murine intestinal neoplasia. Aim 2. Establish that bile acid-induced M3R activation promotes intestinal neoplasia by ERK- mediated gene transcription. Aim 3. Establish that pharmacologic inhibition of M3R mimics the effects of m3r gene ablation and reduces intestinal neoplasia. This revised application includes strong preliminary data supporting our central hypothesis, a focused approach to defining the mechanisms whereby M3R and bile acids promote colon carcinogenesis, unique animal models, innovative methods, and an outstanding group of highly experienced co-investigators and consultants. Based on our provocative preliminary data supporting the key role of M3R in colon tumor formation, it is timely and important to determine whether blocking M3R activation with anti-muscarinic receptor agents mimics the reduction in tumor number observed in M3R-deficient mice. Outcomes will establish the critical role of M3R and advance human health by spurring development of pharmacologic strategies to prevent and treat colon neoplasia by attenuating muscarinic receptor activation. At the same time, fundamental knowledge gained regarding the role of muscarinic receptors in mediating bile acid actions and neoplasia will advance the general area of cancer biology. PUBLIC HEALTH RELEVANCE: For men and women colon cancer is a leading cause of morbidity and mortality;in the US, approximately 150,000 people are diagnosed and 50,000 die from colon cancer each year. Efficacy of treatment for advanced colon cancer is limited and new approaches are needed. It is anticipated that the proposed investigation on the critical role of M3 muscarinic receptors in intestinal neoplasia will reveal a novel, low-risk strategy to prevent colon cancer in high-risk populations (e.g. those with familial adenomatous polyposis syndrome) and to treat this important, frequently deadly disease in those who cannot be cured with surgery.